1. Field of the Invention
The present invention relates to a film formation apparatus for a semiconductor process for forming a silicon nitride film on a target substrate, such as a semiconductor wafer, and also to a method for using the apparatus. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices, a process, such as CVD (Chemical Vapor Deposition), is performed to form a thin film, such as a silicon nitride film, on a target substrate, such as a semiconductor wafer. For example, a film formation process of this kind is arranged to form a thin film on a semiconductor wafer, as follows.
At first, the interior of the process container (reaction tube) of a heat processing apparatus is heated by a heater at a predetermined load temperature, and a wafer boat that holds a plurality of semiconductor wafers is loaded. Then, the interior of the process container is heated up to a predetermined process temperature, and gas inside the process container is exhausted through an exhaust port, so that the pressure inside the process container is decreased to a predetermined pressure.
Then, while the interior of the process container is kept at the predetermined temperature and pressure (kept exhausted), a film formation gas is supplied through a process gas feed line into the process container. For example, in the case of CVD, when a film formation gas is supplied into a process container, the film formation gas causes a thermal reaction and thereby produces reaction products. The reaction products are deposited on the surface of each semiconductor wafer, and form a thin film on the surface of the semiconductor wafer.
Reaction products generated during the film formation process are deposited (adhered) not only on the surface of the semiconductor wafer, but also on, e.g., the inner surface of the process container and other members, the latter being as by-product films. If the film formation process is continued while by-product films are present on the inner surface of the process container, a stress is generated and causes peeling of some of the by-product films and the quartz of the process container due to a difference in coefficient of thermal expansion between the quartz and by-product films. Consequently, particles are generated, and may decrease the yield of semiconductor devices to be fabricated and/or deteriorate some components of the processing apparatus.
In order to solve this problem, cleaning of the interior of the process container is performed after the film formation process is repeated several times. In this cleaning, the interior of the process container is heated at a predetermined temperature by a heater, and a cleaning gas, such as a mixture gas of fluorine and a halogen-containing acidic gas, is supplied into the process container. The by-product films deposited on the inner surface of the process container are thereby dry-etched and removed by the cleaning gas. Jpn. Pat. Appln. KOKAI Publication No. 3-293726 discloses a cleaning method of this kind.
In order to prevent particle generation in a heat processing apparatus, it is preferable to frequently perform cleaning thereon, e.g., to clean the interior of the heat processing apparatus every time a thin film is formed on semiconductor wafers. However, in this case, the downtime of the heat processing apparatus becomes larger and thereby deteriorates productivity.